Implemented basic SurfaceClosure compression for storing per-vertex.

This is really simple, and doesn't account for things like constant
parameters yet.  It's just to get things rolling.

src/color.rs

@@ -5,7 +5,9 @@ pub use color::{
     xyz_to_rec709_e,
 };
 use float4::Float4;
+use half::f16;
 use spectral_upsampling::meng::{spectrum_xyz_to_p_4, EQUAL_ENERGY_REFLECTANCE};
+use trifloat::signed48;
 
 use crate::{lerp::Lerp, math::fast_exp};
 
@@ -138,6 +140,115 @@ impl Color {
             Color::Temperature { factor, .. } => factor,
         }
     }
+
+    /// Returns the post-compression size of this color.
+    pub fn compressed_size(&self) -> usize {
+        match self {
+            Color::XYZ(_, _, _) => 7,
+
+            Color::Blackbody { .. } => 5,
+
+            Color::Temperature { .. } => 5,
+        }
+    }
+
+    /// Writes the compressed form of this color to `out_data`.
+    ///
+    /// `out_data` must be at least `compressed_size()` bytes long, otherwise
+    /// this method will panic.
+    ///
+    /// Returns the number of bytes written.
+    pub fn write_compressed(&self, out_data: &mut [u8]) -> usize {
+        match *self {
+            Color::XYZ(x, y, z) => {
+                out_data[0] = 0; // Discriminant
+                let col = signed48::encode((x, y, z));
+                let col = col.to_le_bytes();
+                (&mut out_data[1..7]).copy_from_slice(&col[0..6]);
+            }
+
+            Color::Blackbody {
+                temperature,
+                factor,
+            } => {
+                out_data[0] = 1; // Discriminant
+                let tmp = (temperature.min(std::u16::MAX as f32) as u16).to_le_bytes();
+                let fac = f16::from_f32(factor).to_bits().to_le_bytes();
+                out_data[1] = tmp[0];
+                out_data[2] = tmp[1];
+                out_data[3] = fac[0];
+                out_data[4] = fac[1];
+            }
+
+            Color::Temperature {
+                temperature,
+                factor,
+            } => {
+                out_data[0] = 2; // Discriminant
+                let tmp = (temperature.min(std::u16::MAX as f32) as u16).to_le_bytes();
+                let fac = f16::from_f32(factor).to_bits().to_le_bytes();
+                out_data[1] = tmp[0];
+                out_data[2] = tmp[1];
+                out_data[3] = fac[0];
+                out_data[4] = fac[1];
+            }
+        }
+        self.compressed_size()
+    }
+
+    /// Constructs a Color from compressed color data, and also returns the
+    /// number of bytes consumed from `in_data`.
+    pub fn from_compressed(in_data: &[u8]) -> (Color, usize) {
+        match in_data[0] {
+            0 => {
+                // XYZ
+                let mut bytes = [0u8; 8];
+                (&mut bytes[0..6]).copy_from_slice(&in_data[1..7]);
+                let (x, y, z) = signed48::decode(u64::from_le_bytes(bytes));
+                (Color::XYZ(x, y, z), 7)
+            }
+
+            1 => {
+                // Blackbody
+                let mut tmp = [0u8; 2];
+                let mut fac = [0u8; 2];
+                tmp[0] = in_data[1];
+                tmp[1] = in_data[2];
+                fac[0] = in_data[3];
+                fac[1] = in_data[4];
+                let tmp = u16::from_le_bytes(tmp);
+                let fac = f16::from_bits(u16::from_le_bytes(fac));
+                (
+                    Color::Blackbody {
+                        temperature: tmp as f32,
+                        factor: fac.into(),
+                    },
+                    5,
+                )
+            }
+
+            2 => {
+                // Temperature
+                let mut tmp = [0u8; 2];
+                let mut fac = [0u8; 2];
+                tmp[0] = in_data[1];
+                tmp[1] = in_data[2];
+                fac[0] = in_data[3];
+                fac[1] = in_data[4];
+                let tmp = u16::from_le_bytes(tmp);
+                let fac = f16::from_bits(u16::from_le_bytes(fac));
+                (
+                    Color::Temperature {
+                        temperature: tmp as f32,
+                        factor: fac.into(),
+                    },
+                    5,
+                )
+            }
+
+            _ => unreachable!(),
+        }
+    }
 }
 
 impl Mul<f32> for Color {

src/shading/mod.rs

@@ -4,7 +4,7 @@ use std::fmt::Debug;
 
 use crate::{color::Color, surface::SurfaceIntersectionData};
 
-use self::surface_closure::SurfaceClosure;
+pub use self::surface_closure::SurfaceClosure;
 
 /// Trait for surface shaders.
 pub trait SurfaceShader: Debug + Sync {

src/shading/surface_closure.rs

@@ -6,7 +6,7 @@ use float4::Float4;
 
 use crate::{
     color::{Color, SpectralSample},
-    lerp::lerp,
+    lerp::{lerp, Lerp},
     math::{clamp, dot, zup_to_vec, Normal, Vector},
     sampling::cosine_sample_hemisphere,
 };
@@ -153,6 +153,128 @@ impl SurfaceClosure {
             ),
         }
     }
+
+    /// Returns the post-compression size of this closure.
+    pub fn compressed_size(&self) -> usize {
+        1 + match *self {
+            Lambert(color) => color.compressed_size(),
+            GGX { color, .. } => {
+                2 // Roughness
+                + 2 // Fresnel
+                + color.compressed_size() // Color
+            }
+            Emit(color) => color.compressed_size(),
+        }
+    }
+
+    /// Writes the compressed form of this closure to `out_data`.
+    ///
+    /// `out_data` must be at least `compressed_size()` bytes long, otherwise
+    /// this method will panic.
+    ///
+    /// Returns the number of bytes written.
+    pub fn write_compressed(&self, out_data: &mut [u8]) -> usize {
+        match *self {
+            Lambert(color) => {
+                out_data[0] = 0; // Discriminant
+                color.write_compressed(&mut out_data[1..]);
+            }
+            GGX {
+                color,
+                roughness,
+                fresnel,
+            } => {
+                out_data[0] = 1; // Discriminant
+
+                // Roughness and fresnel (we write these first because they are
+                // constant-size, whereas the color is variable-size, so this
+                // makes things a little easier).
+                let rgh =
+                    ((roughness.max(0.0).min(1.0) * std::u16::MAX as f32) as u16).to_le_bytes();
+                let frs = ((fresnel.max(0.0).min(1.0) * std::u16::MAX as f32) as u16).to_le_bytes();
+                out_data[1] = rgh[0];
+                out_data[2] = rgh[1];
+                out_data[3] = frs[0];
+                out_data[4] = frs[1];
+
+                // Color
+                color.write_compressed(&mut out_data[5..]); // Color
+            }
+            Emit(color) => {
+                out_data[0] = 2; // Discriminant
+                color.write_compressed(&mut out_data[1..]);
+            }
+        }
+        self.compressed_size()
+    }
+
+    /// Constructs a SurfaceClosure from compressed closure data, and also
+    /// returns the number of bytes consumed from `in_data`.
+    pub fn from_compressed(in_data: &[u8]) -> (SurfaceClosure, usize) {
+        match in_data[0] {
+            0 => {
+                // Lambert
+                let (col, size) = Color::from_compressed(&in_data[1..]);
+                (SurfaceClosure::Lambert(col), 1 + size)
+            }
+
+            1 => {
+                // GGX
+                let mut rgh = [0u8; 2];
+                let mut frs = [0u8; 2];
+                rgh[0] = in_data[1];
+                rgh[1] = in_data[2];
+                frs[0] = in_data[3];
+                frs[1] = in_data[4];
+                let rgh = u16::from_le_bytes(rgh) as f32 * (1.0 / std::u16::MAX as f32);
+                let frs = u16::from_le_bytes(frs) as f32 * (1.0 / std::u16::MAX as f32);
+                let (col, size) = Color::from_compressed(&in_data[5..]);
+                (
+                    SurfaceClosure::GGX {
+                        color: col,
+                        roughness: rgh,
+                        fresnel: frs,
+                    },
+                    5 + size,
+                )
+            }
+
+            2 => {
+                // Emit
+                let (col, size) = Color::from_compressed(&in_data[1..]);
+                (SurfaceClosure::Emit(col), 1 + size)
+            }
+
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl Lerp for SurfaceClosure {
+    fn lerp(self, other: SurfaceClosure, alpha: f32) -> SurfaceClosure {
+        match (self, other) {
+            (Lambert(col1), Lambert(col2)) => Lambert(lerp(col1, col2, alpha)),
+            (
+                GGX {
+                    color: col1,
+                    roughness: rgh1,
+                    fresnel: frs1,
+                },
+                GGX {
+                    color: col2,
+                    roughness: rgh2,
+                    fresnel: frs2,
+                },
+            ) => GGX {
+                color: lerp(col1, col2, alpha),
+                roughness: lerp(rgh1, rgh2, alpha),
+                fresnel: lerp(frs1, frs2, alpha),
+            },
+            (Emit(col1), Emit(col2)) => Emit(lerp(col1, col2, alpha)),
+
+            _ => panic!("Cannot lerp between different surface closure types."),
+        }
+    }
 }
 
 /// Lambert closure code.

src/surface/micropoly_batch.rs

@@ -11,7 +11,7 @@ use crate::{
     lerp::lerp_slice,
     math::{cross, dot, Matrix4x4, Normal, Point},
     ray::{RayBatch, RayStack},
-    shading::{SimpleSurfaceShader, SurfaceShader},
+    shading::SurfaceClosure,
 };
 
 use super::{triangle, SurfaceIntersection, SurfaceIntersectionData};
@@ -33,7 +33,9 @@ pub struct MicropolyBatch<'a> {
     normals: &'a [Normal],
 
     // Per-vertex shading data.
-    vertex_closures: &'a [SimpleSurfaceShader],
+    compressed_vertex_closure_size: usize, // Size in bites of a single compressed closure
+    vertex_closure_time_sample_count: usize,
+    compressed_vertex_closures: &'a [u8], // Packed compressed closures
 
     // Micro-triangle indices.  Each element of the tuple specifies the index
     // of a vertex, which indexes into all of the arrays above.
@@ -127,7 +129,9 @@ impl<'a> MicropolyBatch<'a> {
             time_sample_count: time_sample_count,
             vertices: vertices,
             normals: normals,
-            vertex_closures: &[],
+            compressed_vertex_closure_size: 0,
+            vertex_closure_time_sample_count: 1,
+            compressed_vertex_closures: &[],
             indices: indices,
             accel: accel,
         }
@@ -317,8 +321,16 @@ impl<'a> MicropolyBatch<'a> {
 
                         // Calculate interpolated surface closure.
                         // TODO: actually interpolate.
-                        let closure = self.vertex_closures
+                        let closure = {
-                            [hit_tri_indices.0 as usize * self.time_sample_count];
+                            let start_byte = hit_tri_indices.0 as usize
+                                * self.compressed_vertex_closure_size
+                                * self.vertex_closure_time_sample_count;
+                            let end_byte = start_byte + self.compressed_vertex_closure_size;
+                            let (closure, _) = SurfaceClosure::from_compressed(
+                                &self.compressed_vertex_closures[start_byte..end_byte],
+                            );
+                            closure
+                        };
 
                         let intersection_data = SurfaceIntersectionData {
                             incoming: rays.dir(ray_idx),
@@ -334,7 +346,7 @@ impl<'a> MicropolyBatch<'a> {
                         // Fill in intersection data
                         isects[ray_idx] = SurfaceIntersection::Hit {
                             intersection_data: intersection_data,
-                            closure: closure.shade(&intersection_data, ray_time),
+                            closure: closure,
                         };
                     }
                 });